The general aim of the proposed study is to elucidate the neuronal circuitry of the dorsal cochlear nucleus (DCN), so that its role in audition can be understood. The DCN is a relatively peripheral, laminated, auditory nucleus that may be considered a miniature, acousitc cerebellum for phylogenetic, onto genetic, and morphological reasons. A series of physiological experiments is proposed that focus on the DCN parallel fibers, a prominant surface fiber tract analogous to the parallel fibers of the cerebellum, and the cells innervated by these fibers, principally fusiform cells, which are analogous to Purkingie cells. These fibers are of interest because they may regulate the output of the DCN. Initially, characterization of DCN field potentials evoked by surface stimulation of the DCN will be made. Current source density analysis will be used to provide evidence that the field potentials are produced by the parallel fibers. Measurements like these will be compared to similar measurements made in other parallel fiber systems in other laminated structures. It is important to demonstrate conclusively that the field potentials are due to synchronized parallel fiber activity. Therefore, attempts will be made to show that the potentials disappear after the parallel fibers between the stimulating and recording electrodes are severed or anesthetized. It is known anatomically that DCN granule cells give rise to parallel fibers, but responses of granule cells to acoustic stimulation are unknown. Therefore, an attempt will be made to antidromically activate, and thus identify, granule cells in a region of the cochlear nucleus where they are numerous, and then study responses of these cells to acoustic stimuli. Other experiments involve recordings from single units located near the path of the parallel fibers. Recordings will be made of responses to acoustic stimulation and/or antidromic activation so that the effects of the parallel fibers on the responsiveness of DCN cells (especially fusiform cells) to these stimuli can be assessed. The results obtained will be essential in determining the neuronal circuitry of the DCN and will lead to a better understanding of this complex auditory nucleus.